1. Technical Field
The present application relates to the packaging of a semiconductor die and more particularly to the repairing of delaminations within the package.
2. Description of the Related Art
Integrated circuits are formed on wafers of semiconductor material. On a typical semiconductor wafer, many identical integrated circuits are formed. The wafer is then diced, namely, cut into many dice, each die comprising an integrated circuit.
The die is usually then packaged to protect it from physical damage and to place it in a form which can be easily installed in a system of which it will be a part. FIG. 1A illustrates a side view of a typical packaged integrated circuit. The package 20 comprises a lead frame 21 and a semiconductor die 24 bonded to a die pad 26 of the lead frame 21 by an adhesive layer 28. Wires 30 are coupled between the die 24 and leads 33 by a wire bonding process. Molding compound 32 covers the die 24 and protects it from outside elements. A heat sink may also be provided in the package 20.
FIG. 1B illustrates another typical semiconductor package 20, the flip chip ball grid array. Solder bumps 36 are attached to contact pads (not shown) of die 24. The die 24 is mounted on substrate 38 with the solder bumps 36 in electrical contact with pads (not shown) of the substrate 38. An epoxy underfill 40 fills the gaps between the solder bumps 36, the die 24, and the substrate 38. Molding compound 32 covers the die 24, and the underfill 40. Solder balls 42 are attached to the surface of the substrate 38 opposite the solder bumps 36.
For both types of packages, while the packaging protects the die 24 from many kinds of damage, the packaging subjects the die 24 to other risks. The package 20 goes through many cycles of heating and cooling throughout its lifetime. The molding compound 32 typically must be in a liquid state when it is first applied and thus it must be at a temperature above its melting point. The liquid molding compound 32 covers the die 24 and the lead frame 21 or substrate 38 heating both the die 24 and the lead frame 21 or substrate 38. The molding compound 32 then is cooled and becomes a solid bonded to both the die 24 and the lead frame 21 or substrate 38, thereby encapsulating the integrated circuit into a final semiconductor product. At this point the semiconductor product may be subject to testing during which the package 20 heats up, then cools, after which it is further tested to ensure that the integrated circuit is functional and that the package 20 is intact. Thus before the integrated circuit is ever sold it is usually subjected to one or more heating/cooling cycles. In some testing, the semiconductor products are subjected to a burn-in cycle in which the packages are heated and cooled from external sources for many cycles, during which time they are tested for operation.
When the die 24 is in its operating environment, it is again subjected to many cycles of heating and cooling. Each time the integrated circuit is turned on and in use the die 24 may become very hot. The heating of the die 24 causes the lead frame 21/substrate 38 and the molding compound 32 to become hot as well. When the integrated circuit turns off, the die 24, the substrate 38, and the molding compound 32 cool once again. The package 20 may also become hot or cool based on the physical environment in which it is placed.
When the die 24 is heated or cooled, it expands or shrinks according to a coefficient of thermal expansion (CTE) particular to the material of the die 24. Each component of the integrated circuit package 20 typically has a different CTE. A material with a high CTE will expand or shrink more than a material with a lower CTE under a given increase or decrease in temperature. When the package 20 is heated or cooled, the molding compound 32, the die 24, and the lead frame 21 or substrate 38 expand or contract differently from each other. This disparity in expansion causes the die 24 to experience compressive, expansive, and tensile forces. The stress is greater at the edges and corners of the die 24. It is important that the integrity of the package be maintained to prevent the integrated circuit from failing.